Differences in frequency and regulation of T follicular helper cells between newly diagnosed and chronic pediatric immune thrombocytopenia.

OBJECTIVE: This study aims to investigate the role of T follicular helper (TFH) cells in the immunopathogenesis of pediatric immune thrombocytopenia (ITP), as well as differences in TFH expansion and its regulation between newly diagnosed ITP (nITP) and chronic pediatric ITP (cITP).

METHODS: Eighty-five children with ITP and 20 age-matched healthy controls were enrolled into this study. TFH cell frequencies and TFH cell-associated regulatory factors before and after treatment were analyzed by flow cytometry, RT-PCR and ELISA.

RESULTS: The percentages of TFH cells were significantly elevated in both nITP and cITP compared with controls. RT-PCR revealed significant differences in Bcl-6, c-Maf, Blimp-1, ICOSL, TACI and BAFFR mRNA expression in CD4(+) T or CD19(+) B cells between patients and controls, and further between nITP and cITP, before and after treatment. Moreover, there were significant differences in serum IL-4, IL-21 and BAFF between patients and controls.

CONCLUSION: The overactivation of TFH cells may contribute to the immunopathogenesis of pediatric ITP. IL-21 and IL-4 serum levels may affect the differentiation of TFH cells in ITP patients. The aberrant balance between BAFFR-BAFF/TACI-BAFF may be a factor that caused the persistent high expression of ICOSL in pediatric cITP, which consequently lead to the over activation of TFH cells in pediatric cITP.